Radovan Not quite. Graphene is a 3d material but has periodicity in 2d making its symmetry given by one of the 80 subperiodic layer groups. Mike Glazer
Get Outlook for Android<https://aka.ms/AAb9ysg> ________________________________ From: rietveld_l-requ...@ill.fr <rietveld_l-requ...@ill.fr> on behalf of Radovan Cerny <radovan.ce...@unige.ch> Sent: Friday, December 30, 2022 11:07:52 AM To: Matthew Rowles <rowle...@gmail.com> Cc: RIETVELD_L Distribution List <rietveld_l@ill.fr> Subject: RE: "2d materials don't exist" editorial?? Thank you Matt, for bringing this subject which I have never taken too seriously, butt as Massimo pointed out in his paper, there are important differences in what symmetry allows for 2D and what for 2P, for example. I feel now a bit responsible, because my colleagues at the Quantum matter dpt. at UNIGE are working on layered pnictides and call them always 2D materials, which is not correct. They are 2P materials. I will try to educate them now, even if I am retired. Maybe they can call them 2D materials if they talk about the physical properties rather than about the structure? I have already tried to introduce then in the OD theory for polytypic structures, but without too much success. They prefer to do their DFT modelling rather than have a look on what has been already done. A test, whether I have properly understood Massimo: Graphen is 2D material, but when I attach anything to it or take more than one layer of graphen, it becomes 2P material, right? Have a nice end of the year Radovan Radovan Cerny Laboratoire de Cristallographie Université de Genève 24, quai Ernest-Ansermet CH-1211 Geneva 4, Switzerland Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 mailto : radovan.ce...@unige.ch<mailto:radovan.ce...@unige.ch> URL : http://www.unige.ch/sciences/crystal/cerny/rcerny.htm ________________________________ De : rietveld_l-requ...@ill.fr <rietveld_l-requ...@ill.fr> de la part de Matthew Rowles <rowle...@gmail.com> Envoyé : lundi 26 décembre 2022 11:08 À : Alan W Hewat <alan.he...@neutronoptics.com> Cc : Leopoldo Suescun <leopo...@fq.edu.uy>; RIETVELD_L Distribution List <rietveld_l@ill.fr> Objet : Re: "2d materials don't exist" editorial?? These are good learning events. . And it doesn't make much third dimensional periodicity to make a layered material act as a bulk 3d material (see recent publications by Kate Putman), or at least from a powder diffraction point of view. On Sun, 25 Dec 2022, 12:40 Alan W Hewat, <alan.he...@neutronoptics.com<mailto:alan.he...@neutronoptics.com>> wrote: Symmetry is the Crystallographer's first love, but periodicity is more important in deciding to call a structure 2D or 3D. Powder diffraction in particular showed that symmetry is ephemeral in many materials, whose symmetry is lowered when they are cooled. This symmetry is just the consequence of averaging over time and space. Yet we remain fascinated by symmetry, sometimes imposing it on Nature when it has no physical consequences. Great to have a little philosophy to go with the Christmas pudding. Thanks Mathew. ________________________________ Dr Alan Hewat, NeutronOptics Grenoble, FRANCE (from phone) alan.he...@neutronoptics.com +33.476984168 VAT:FR79499450856 http://NeutronOptics.com/hewat _______________________________ On Sun, 25 Dec 2022, 01:16 Matthew Rowles, <rowle...@gmail.com<mailto:rowle...@gmail.com>> wrote: I didn't even know of the existence of the frieze, rod, and layer groups until I read this comment. So, I guess it's working? On Sat, 24 Dec 2022, 22:49 Leopoldo Suescun, <leopo...@fq.edu.uy<mailto:leopo...@fq.edu.uy>> wrote: Hi all, Thank you Matt for bringing up this issue. Massimo Nespolo has been fighting for the correct description of structures, specially focusing on symmetry and proper terminology, for years (see his many articles on the misuse of lattice, sublattice, superlattice, etc). He has, as well, been educating crystallographers of all ages in symmetry concepts and use through IUCr's MaThCryst Commision and Internationa School on Fundamental Crystallograpy courses around the world. He'll probably be remembered by many as a Dick Marsh of symmetry. I guess it is the task of all us, crystallographers, to promote the correct use of terminology related to crystal structures, as suggested by IUCr conventions included in IUCr Dictionary and modern literature. https://dictionary.iucr.org/Main_Page Best wishes for all of you that, in a way or another have this as a special week in your calendars, and Happy New Year for all. Leo El sáb, 24 de dic. de 2022 05:01, Matthew Rowles <rowle...@gmail.com<mailto:rowle...@gmail.com>> escribió: Hi all I think this is the one https://scripts.iucr.org/cgi-bin/paper?S1600576721001606 Matthew On Fri, 23 Dec 2022, 10:00 Matthew Rowles, <rowle...@gmail.com<mailto:rowle...@gmail.com>> wrote: This might be it, but the link is to the iucr homepage: Google: "letter to the editor" two-dimensional "layer groups" graphene iucr [image.png] On Fri, 23 Dec 2022 at 09:53, Matthew Rowles <rowle...@gmail.com<mailto:rowle...@gmail.com>> wrote: Hi all A while ago (months, years??) I recall reading an editorial or letter to the editor about materials being referred to as "2D", and how they're actually 3D, and just periodic in the plane, and should be referred to as 2P and a relevant layer group. Does anyone recall such a thing? Thanks Matthew ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr<mailto:lists...@ill.fr>> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Please do NOT attach files to the whole list <alan.he...@neutronoptics.com> Send commands to <lists...@ill.fr<mailto:lists...@ill.fr>> eg: HELP as the subject with no body text The Rietveld_L list archive is on http://www.mail-archive.com/rietveld_l@ill.fr/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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